The visual process (dim light vision) is mediated by the glycoprotein rhodopsin. Absorption of a photon by a molecule of rhodopsin results in the isomerization of the chromophore 11-cis-retinal to all-trans.-retinal. Subsequent dark reactions lead to visual excitation and ultimately to information processing in the brain. The mechanism by which rhodopsin indicates the visual excitation is poorly understood and is a major focus of this proposal. The primary objectives of the work proposed here are to deduce the chemical and structural interactions mediating visual excitation. Further, as rhodopsin is a membrane protein we are also investigating the participation of the membrane in the overall process. We have tried to put together a broad based approach for the elucidation of the mechanism of action of rhodopsin. The studies described are designed to investigate both the dynamic and static properties of opsin and rhodopsin. A major focus of our work is the regeneration of rhodopsin from 11-cis-retinal and opsin as any bonds or interactions formed during regeneration must be broken following absorption of a photon. Further our previous studies have established that sodium cholate solubilized rhodopsin is very similar in most characteristics to rhodopsin bound to the ROS membrane. Studies proposed include the effect of phospholipid composition, cholate concentration, temperature and 11-cis-retinal analogues on the kinetics of regeneration. In addition we also plan to investigate the effect of cholate concentration of the photochemically induced conversion of meta I to meta II. Finally, we are proposing a comparative study of rhodopsin and opsin solubilized from a variety of sources. It is the goal of this latter investigation to obtain a form of rhodopsin amenable to detailed structural studies.